1. Field Of The Invention
This invention relates to a method of fabricating iridium-containing material structures on substrates, such as Ir-based electrode structures for microelectronic devices and subassemblies.
2. Description of the Related Art
Conducting metal and metal oxide electrodes are preferred for the integration of devices based on perovskite and high dielectric constant oxide materials. The electrode identity may influence the crystallographic orientation, the growth of the capacitor film or other device structures formed over or on the electrode, the leakage properties of the device structure, the stability of the device toward temperature and humidity, and the long term reliability of the device. The incorporation and use of the electrode requires that the electrode material be easily deposited in high purity, easily patterned and etched, and readily integrated for complete device build and performance. The importance of the electrode cannot be overstated, relative to device performance and ease of fabrication of the overall device structure.
Iridium (Ir) and iridium oxide (IrO.sub.2) are of great interest for use as electrode materials in both dynamic random access memories (DRAMs) and for ferroelectric-based memory devices (FRAMs) which incorporate perovskite metal oxide thin-films as the capacitor layer.
The advantages of Ir over other possible electrode materials include ease of deposition including the formation of the electrode using chemical vapor deposition (CVD), the ability to "dry etch" the material, the ability to form a stable conducting oxide at high temperatures in an oxidizing environment, the ability to convert IrO.sub.2 back to Ir metal at 350.degree. C. in forming gas, and the ability to operate stably at high temperatures in a working device with a high degree of reliability.
The deposition and processing of Ir-based electrodes is highly desirable based on these advantages. The metal displays a resistivity of 5.3 .mu..omega.-cm at 20.degree. C. and IrO.sub.2 is highly conducting with a reported resistivity of 100 .mu..OMEGA.-cm. The formation of IrO.sub.2 occurs only at elevated temperatures (&gt;550.degree. C.) in O.sub.2 and is a superior material for the deposition of complex oxide for dielectric or ferroelectric capacitors. Further, during the high temperature CVD process for the growth of these capacitors, the formation of IrO.sub.2 can be advantageous for limiting inter-diffusion, as for example by acting as a diffusion barrier to oxidation of conducting polysilicon vias or plugs. IrO.sub.2 is a material which therefore has many advantages in forming a robust, low-leakage electrode for reliable device fabrication.
Based on the need for Ir-based electrodes, a facile etching method for Ir is critical to commercial incorporation of Ir into manufacturing, enabling the use of CVD techniques which are especially desired for electrode structures with dimensional characteristics below 0.5 micron. In order to obtain useful electrode structures, it is generally necessary to etch the deposited Ir-based material, to form bottom or top electrode elements of the desired dimensional and positional character. The etching method should therefore be readily employed to define useful electrode patterns of the desired critical dimensions. A commercially useful "dry etch" methodology applicable to Ir-based electrodes would permit such electrodes to be economically fabricated for use in a variety of microelectronic applications, structures and devices, and would constitute a substantial advance in the art relative to conventional use of platinum electrodes.
The art has variously disclosed the chemical vapor deposition of iridium for the manufacture of electronic devices in a reducing atmosphere such as hydrogen gas environment. The art has taught the use of such reducing atmosphere for the purpose of achieving the deposition of element metal iridium for electrodes in applications in which high temperature dielectric materials (e.g., SBT, BST, PZT, PLZT, PNZT, LaCaMnO.sub.3, etc., where SBT=strontium bismuth tantalate, BST=barium strontium titanate, PZT=lead zirconium titantate, PLZT=lead lanthanum zirconium titanate, and PNZT=lead niobium zirconium titanate) are deposited on the electrode, to minimize the possibility of degradation of the electrode in such applications.
In the context of the foregoing circumstances, the art has sought improvements in process technology for the formation of semiconductor and ferroelectric structures which employ Ir electrodes, specifically as associated with the fabrication of complex dielectric and ferroelectric material layers and structures.
It is an object of the present invention to provide a process for the formation of iridiumbased electrodes which achieves a material simplification in fabrication efficiency and cost, and which achieves an electrode structure for dielectric structures which is highly advantageous for integration, efficient and readily fabricated.
It is another object of the invention to provide a ready and simply applied method for the patterning and fabrication of Ir-containing structures such as electrodes or contacts onto substrates.
It is yet another object of the invention to provide a simplified method for the fabrication of metal oxide thin film capacitor structures including iridium, iridium oxide or iridium-containing electrode elements.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.